1. Field of the Invention
The invention relates to a method for operating a print further processing system for producing and processing printed products, in particular for forming stacks or packs of printed product collections comprising completed final printed products such as periodicals and newspapers, which are preferably put together from a main product and a plurality of part products and/or inserts. The present invention relates, furthermore, to a print further processing system for implementing the method.
With the increasing regionalization or individualization of products, higher and higher requirements are being placed on print further processing. On the one hand, in order to increase profitability, processing capacities have to be increased in step with the increased capacities of the rotary system, on the other hand it must also be possible to make the products without difficulty finished and ready to ship for extremely small zones. The smaller the zones, which means regions with the same collection (for example main and part products with zone-specific advertising inserts, official notices and/or references to events), the more part packs, which means packs comprising a few products, have to be processed. Since the processing cycle in the case of the known stacking apparatuses, binders and so on cannot be reduced below a cycle time of currently about 2 seconds, exactly the same amount of time is needed for the production of a pack having a few printed products or collections of printed products as for a complete pack with the complete number of printed products or collections which, depending on the thickness of the printed products or collections, can be around 20 to 40 or more. The more small stacks or packs have to be formed, the more inefficiently the known systems for print further processing operate.
2. Discussion of Related Art
EP 1 935 821 A1 discloses a method for forming stacks from print shop products, such as in particular books, periodicals, newspapers, brochures or similar products, which are produced industrially on production lines. Such production lines are formed by individual machines arranged serially one after another and coupled to one another, each of these individual machines having a maximum production speed depending on the product parameters and production conditions. In EP 1 935 821 A1, it is described as disadvantageous that the maximum possible production speed of the overall production lines according to the prior art is therefore limited by the machine having the lowest maximum speed. It is viewed as a particularly difficult situation if product parameters which have an influence on the maximum production speed of the machine that limits the maximum production speed of the production line change continuously during the production. This may be the case, for example, in a stacking apparatus which is intended to form stacks of different size, depending on the order quantities of various recipients. To this end, it is explained that, for one stacking apparatus, there are two upper production limits which cannot be exceeded. The first limit relates to the maximum possible rate at which the printed products can be accepted by the stacking apparatus. The second limit relates to the maximum possible rate or the minimum possible cycle time during which stacks can be conveyed out of the stacking apparatus.
In EP 1 935 821 A1, on the basis of the finding that the maximum possible feed rate is a multiple of the maximum possible output delivery rate, it is concluded that it is not possible to form any smaller stacks than the ratio, rounded to the nearest whole number, of the maximum possible feed rate divided by the maximum possible output delivery rate. According to a first prior art, provision is made to solve the problem by the printed products being distributed by means of a distribution device to a plurality of stacking apparatuses arranged in parallel and the stacks then being combined again into one line. With sufficiently many stacking apparatuses, it should be possible at any time to process the full production output of the remaining line. However, it is assumed that the great requirement for machines, the additional space required and the worsened accessibility to the individual stacking apparatuses arranged in parallel would be disadvantageous.
In order to avoid these disadvantages and in order to avoid distribution to a plurality of stacking apparatuses arranged in parallel, EP 1 935 821 A1 proposes a method for forming stacks from printed products in which the printed sheets fed in from a plurality along a single conveying section and collated on the latter to form pre-products are then processed into stacks in a single stacking apparatus, the procedure for collating the printed sheets to form pre-products being controlled as a function of the size of the stack of printed products to be formed. This procedure of collating printed sheets to form pre-products is necessarily interrupted when a stack size determined by the number of printed products is undershot, the stack size leading to the interruption to the procedure being determined from the product of the number of cycles of the collating procedure and the minimum cycle time for forming a stack. In a known way, therefore, the knowledge of the maximum processing throughput of the stacking apparatus is utilized in order to trigger a control step when it is exceeded.
Irrespective of the size of the stacks to be formed in the stacking apparatus, the production speed in the production line is kept constantly high. However, the production throughput of the overall production line is still reduced during the formation of small stacks in the stacking apparatus since, although a fluctuation or continuous change in the speed in the production line can be avoided, the overall throughput in this method also has to be reduced to such an extent that there is sufficient time available for the delivery of the stacks. If a disruption or an interruption in the operation of the stacking apparatus occurs, then the throughput of the entire production line has to be reduced to zero.